Cured silicone powders are used as additives in cosmetics, paints, inks, thermosetting organic resins, thermoplastic organic resins, and so forth. They are highly qualified for use as internal stress-relaxing agents for thermosetting (i.e., non-silicone) organic resins and as surface lubricants for organic resin films. Cured silicone powders of this type can be fabricated, for example, by first preparing the water-based emulsion of a curable silicone composition (hereinafter also referred to as a water-based curable SC emulsion), then curing the composition to form the water-based dispersion of a cured silicone powder, and finally removing the water from the water-based dispersion (refer to Japanese Laid Open Patent Application Numbers Sho 63-77942 and Sho 64-70558).
However, the cured silicone powders prepared by the methods taught in Japanese Laid Open Patent Application Numbers Sho 63-77942 and Sho 64-70558 exhibit a poor fluidity and substantial aggregation and blocking tendencies Moreover, these cured silicone powders are poorly dispersible in organic resins and organic solvents.
In response to these problems, Japanese Laid Open Patent Application Number Hei 4-348143 proposes a cured silicone powder whose surface has been coated with a metal oxide micropowder, for example, with silicon oxide. The same application also proposes a method for preparing this cured silicone powder in which a metal oxide sol (e.g., a silicon oxide sol), is added to the water-based dispersion of a cured silicone powder (hereinafter also referred to as a water-based cured SP dispersion) and the resulting mixture is then dewatered. On the other hand, Japanese Laid Open Patent Application Number Hei 5-179144 proposes to solve the aforementioned problems through a method for the preparation of a powder mixture that consists of dewatering the water-based dispersion of a cured silicone powder plus an inorganic micropowder.
The cured silicone powder taught in Japanese Laid Open Patent Application Number Hei 4-348143 is, nevertheless, associated with several drawbacks. Thus, this cured silicone powder still exhibits an inadequate behavior with regard to blocking. Moreover, since it is prepared using a metal oxide sol, the final cured silicone powder product has a high ionic impurity content. Another drawback is that the metal oxide micropowder is readily shed by the cured silicone powder when the powder is subjected to shear force. Comparative Example 2 in Japanese Laid Open Patent Application Number Hei 4-348143 describes the production of cured silicone powder by dewatering a water-based dispersion prepared by the addition of amorphous silica micropowder to a water-based cured SP dispersion. However, this particular cured silicone powder still exhibits inadequate flow, dispersion, aggregation, and blocking characteristics because the amorphous silica micropowder is adhered in a simple manner on the surface of the cured silicone powder. Moreover, this cured silicone powder also readily sheds the amorphous silica micropowder when subjected to shear force. In the case of the method for preparing a powder mixture that is disclosed in Japanese Laid Open Patent Application Number Hei 5-179144, the resulting powder mixture is nothing more than a simple mixture of the cured silicone powder and inorganic micropowder, and as a result it again exhibits inadequate flow, dispersion, aggregation, and blocking characteristics. Another drawback in this case is that the inorganic micropowder readily separates from the powder mixture.